This invention relates to a multichannel magnetic head of an AC excitation type, and more particularly to a multichannel magnetic and optical head of a structure comprising optical fibers arranged in a row on the multichannel magnetic head which can simultaneously linearly read magnetic patterns and optical patterns of the same location of an object of detection.
Magnetic heads are widely used for reading data recorded on magnetic cards or a tape, or data printed in readable magnetic ink on a note. The prior art magnetic heads are classified into two types, i.e. an AC excitation type and a DC excitation type, and have the following features.
FIG. 1 shows an AC excitation type magnetic head 100 comprising a magnetic ore 101 of the shape of twin E letters of which central bridge arm 102 is wound with a primary coil 103. The primary coil 103 is connected to an AC power source 104. The magnetic core 101 is wound with the secondary coil 105 on the upper side thereof and with a cancellation coil 106 on the lower side thereof. An object 110 of detection such as a not is adapted to pass above the magnetic core 101.
In the structure above explained, the primary coil 103 is excited with the AC power source 104, and when the object 110 of detection including a magnetic member passes above the upper surface of the magnetic core 101, signals corresponding to the magnetic intensity or the pattern of the magnetic member are outputted from the secondary coil 105. The difference between the above output and the output from the cancellation coil 106 is extracted as magnetic signals in order to remove noise components and bias components arising out of fluctuations in the AC power source 104 and in temperature characteristics of the magnetic core 101.
Since the prior art AC excitation type magnetic head has a magnetic core 101 which is wound with both the secondary coil 105 and the cancellation coil 106, the size of the structure becomes inconveniently big, and when the object 110 as a whole is to be detected simultaneously, a plurality of magnetic heads 100 must be arranged at intervals as shown in FIG. 2. The detection range therefore becomes discrete and incapable of detecting objects at a high precision. This presents a problem in the detection of notes and other objects where highly precise detection is a prerequisite.
FIG. 3 shows a DC excitation magnetic head 120 comprising a magnetic core 121 of the shape of an inverted letter U and an arm of which is wound with an exciting coil 122. The exciting coil 122 is supplied with a DC constant current I. When the object 110 of detection passes above the detection head plane, differential signals are obtained as detection signals V in correspondence to the chronological change on the magnetic member equivalent to the DC component cut off by a capacitor 123.
The DC excitation magnetic head 120 has problems in that as the detection signal V is obtained as a chronological change on the magnetic member, it cannot detect objects which are stationary and moreover has problems in that the level of detection signals changes depending on the relative speed of the object. Since the DC excitation magnetic head 120 is of a small size, some systems have plural heads arranged in a row to cover a wide range. Due to the above mentioned fatal defect, the head cannot be applied to the detection of the magnetic intensity or the magnetic pattern on notes.
There have been proposed in the prior art other optical sensors such as those shown in FIGS. 4 and 5, respectively. In the optical sensor shown in FIG. 4, the light from a light emitting element 130 is focused by a lens 131 for projection on a recording medium 132, and the light reflected from the recording medium 132 is focused on a light receiving element 134 for detection. In the sensor shown in FIG. 5, the light from a light emitting element 135 is focused by a lens 136 for projection on the recording medium 132 and for passing through the recording medium 132, and the transmitted light is focused by a lens 137 for inputting into a light receiving element 138 to thereby read the pattern defined in optical density variations on the recording medium 132.
As the simultaneous formation of a magnetic pattern and an optical pattern on the recording medium 132 became possible in recent years by mixing magnetic powder with print ink, the aforementioned magnetic sensor and optical sensor can now be incorporated in one system for reading the magnetic pattern and the optical pattern concurrently. However, the system is not integrally structured and is incapable of reading the same spot on data at the same time of the above two types of patterns.